Two-speed motor-bike drive

ABSTRACT

A two-speed chain transmission for minibikes, as original equipment or as a conversion kit. High- and low-speed sprockets on a jackshaft are chain driven at different speeds by high and low drive sprockets carried by a centrifugal clutch on the engine shaft. The jackshaft is chain connected to the rear wheel of the bike. The low speed driven sprocket is mounted on the jackshaft by an overrunning clutch which permits the jackshaft to overrun the low drive when it is driven by the high drive. The high-speed sprocket is mounted on the jackshaft by a clutch which is disengageable to let the low-speed drive takeover. A brake acts on the jackshaft on the driven side of the clutches.

United States Patent 3/1949 Gredell Primary Examiner-Benjamin W. WycheAttorney-Trask, Jenkins & Hanley ABSTRACT: A two-speed chaintransmission for minibikes, as original equipment or as a conversionkit. l-lighand lowspeed sprockets on a jackshaft are chain driven atdifferent speeds by high and low drive sprockets carried by acentrifugal clutch on the engine shaft. The jackshaft is chain connectedto the rear wheel of the bike. The low speed driven sprocket is mountedon the jackshaft by an overrunning clutch which permits the jackshaft tooverrun the low drive when it is driven by the high drive. Thehigh-speed sprocket is mounted on the jackshaft by a clutch which isdisengageable to let the lowspeed drive takeover. A brake acts on thejackshaft on the driven side of the clutches.

PATENTEUJUN nan 8,581,853

v sum 1 or 2" v 48 f I 54 INVENTOR STEPHEN J. HOFF BY 214. 4% v 4%ATTORNEYS PATENIED JUN 1 I9" SHEET 2 0F 2 Fig-1 INVENTOR STEPHEN J. HOFFBY MMVAAZ;

ATTORNEYS TWO-SPEED MOTOR-BIKE DRIVE This invention relates to atwo-speed transmission for motorbikes of the type commonly referred toas minibikes. The transmission may be used as original equipment or maybe supplied as a conversion kit.

Minibikes in their simplest form comprise an internal combustion enginewhich through a centrifugal clutch and chain drives the rear wheel. Someunits include a jackshaft in the drive train. The present inventionutilizes a jackshaft connected by a drive chain to the rear drive wheel.The engine shaft carries a centrifugal clutch which drives high-speedand low-speed drive sprockets connected by chains at different speedratios to high-speed and low-speed driven sprockets on the jackshaft.One of the low-speed sprockets is connected to its shaft through anoverrunning clutch which allows the jackshaft to overrun the low-speeddrive train when the highspeed drive train is operative; and one of thehigh-speed sprockets is connected to its shaft by a releasable clutchwhich permits the low-speed drive train to take over the drive when thehigh-speed drive train is declutched.

The overrunning and releasable clutches have the effect of isolating therear drive wheel from the motor shaft and of preventing the motor fromexerting a braking effect, and a brake is desirably provided on thejackshaft at a position beyond the point at which such isolation occurs.

The invention contemplates providing the transmission in a conversionkit for application to single-speed bikes. Such a kit may include amounting bracket which fits between the engine and its frame support.Such bracket carries bearings for the jackshaft, an anchor for the fixedparts of the brake, and a support for the operating control of thereleasable clutch. The kit also includes a centrifugal clutch anddrive-sprocket assembly to be mounted on the engine shaft, the jackshaftand its sprockets, and the overrunning and releasable clutches. Chainsmay be included, or left for the purchaser to obtain from stock sources.

. The accompanying drawings illustrate the invention and show apreferred embodiment. In such drawings:

FIG. 1 is a pictorial view of a minibike equipped with a twospeedtransmission in accordance with the invention;

FIG. 2 is an isometric view of a conversion kit embodying the invention,with the parts shown in operative relationship;

FIG. 3 is a rear elevation of the assembly shown in FIG. 2;

FIG. 4 is a plan view of the assembly shown in FIG. 2, with the shaftspacing shortened for convenient illustration; and

FIG. 5 is an end view of the brake, taken on the line 5-5 of FIG. 4.

The motorbike shown in FIG. 1 comprises a frame having a platform 12supporting an engine 14. The frame is pivoted to a steering fork 16mounted on the front wheel 18 and controlled by handlebars 20. The motor14 drives a centrifugal clutch 22 which is connected by high and lowdrive chains to a jackshaft 24 which in turn is connected by a drive'chain not shown to the rear wheel 26 of the bike.

As shown in FIGS. 2 and 4, the motor shaft carries the hub 30 of acentrifugal clutch having drive shoes 32 which are normally disengagedbut which under centrifugal force move outward into engagement with adriven clutch drum 34. Such drum 34 is carried by a sprocket hub 36rotatable on a bearing sleeve 38 carried by the motor shaft 15 and fixedto the hub 30. The sprocket hub 36 carries a fixed low-speed sprocket 40and a fixed high-speed sprocket 42, which may be of the same size asshown.

The conversion kit shown in FIGS. 2 and 4 comprises a mounting brackethaving a plate 44 adapted to be mounted on the engine platform 12 of thebike and to support the engine 14. At the rear, such plate is bentupward and its top edge carries a tubular-mounting sleeve 46 in whichthe jackshaft 48 is mounted by means of suitable bearings 50. A screw 45is threaded through the upward bent portion to position the engine onthe platform.

The jackshaft, at its remote end as shown in FIG. 2, carries a finaldrive sprocket 52 adapted to be connected by a chain to a sprocket onthe rear wheel 26. Outward from such sprocket the jackshaft also carriesa brake drum 54 adapted to be engaged by a band brake 56 carried by anoffset mounting bar 58 welded to the mounting sleeve 46.

A low-speed driven sprocket 60 and a high-speed sprocket 62 are mountedon the jackshaft 48 by means of clutches, in alignment with the highandlow-speed sprockets 40 and 42 carried by the motor shaft 15. Thelow-speed sprocket 60 is fixed on the outer element 63 of an overrunningclutch 64 ofa known type in which rollers 66 clutch such outer elementto a hub 67 in forward drive direction but permit overrunning in theopposite direction. The clutch is arranged to permit the jackshaft 48 tooverrun the low-speed driven sprocket 60 when the jackshaft is driven ata higher speed by the highspeed sprocket 62.

The high-speed sprocket 62 is mounted on and driven from the jackshaft48 by means of a coil spring clutch 68. This comprises a hub 70 whichcarries the sprocket and has an inner bearing sleeve 71 rotatablymounted on the jackshaft 48. The hub 70 is the clutch driving elementand has an outer cylindrical clutch face 72 for engagement with a clutchspring 74. A driven clutch element 76 is mounted in coaxial abuttingrelation with the driving hub 70 and is provided with an outercylindrical surface 78 in alignment with the surface 72 of the hub 70.The driven element 76 is pinned to the jackshaft by a cross pin 77. Theconnecting clutch spring 74 is a close-wound helical spring, wound ofsuch hand that relative rotation of the driving hub 70 in a drivingdirection with respect to the driven element 76 causes the spring towind up and tighten itself onto the cylindrical surfaces 72 and 78, andthus to clutch the driving and driven elements together. The leading endof the spring lies adjacent the sprocket-end of the hub 70 and is bentoutward to a form a control finger 80. Such finger 80 is engaged in anotch 82 in a control sleeve 84 rotatably mounted on the driving anddriven elements 70 and 76 and closely surrounding the spring 74. Thecontrol sleeve 84 has a laterally projecting axial rib 86 by which thecontrol sleeve 84 can be stopped from rotation by projection of acontrol foot 88 into the path of rotation of the rib 86.

The control foot 88 may be the bentover end of a Bowden wire mounted ina sheath 90 supported by a bracket 92 carried by the jackshaft-mountingsleeve 46. As shown in FIG. 1, the Bowden wire clutch control extendsupward to a control knob 94 mounted on the left handlebar 20 of theminibike. A brakeactuating lever 98 on the right handlebar 20 isconnected by a similar Bowden wire 96 to actuate the brake band 56 toapply braking effort to the drum 54.

When the parts described above are mounted for use, the low-speedsprockets 40 and 60 are connected by a low-speed chain 100, and thehigh-speed sprockets 42 and 62 are connected by a high-speed chain 102.

Operation of the two-speed transmission is as follows. Assume that thespeed control knob 94 is pushed in, so that the control foot 88 lies inthe path of rotation of the rib 86 on the control sleeve 84 for thehigh-speed clutch 68. This anchors the leading end of the clutch spring74 against forward rotation, and the relationship is then such thatforward-drive rotation of the driving hub 70 and of the driven element76 tends to unwind the helical spring 74 with respect to its anchoredleading end 80, and therefore permits either or both of the driving ordriven elements to overrun the spring 74 in a forward-drive direction.The high-speed clutch 68 will then be effectively disengaged.

With the engine idling and the shaft 15 rotating at idling speed, theshoes 32 of the centrifugal clutch will be retracted, and no drive willbe transmitted from the engine to the clutch drum 34. When the engine isaccelerated, the clutch shoes 32 are thrown outward by centrifugal forceto engage the drum 34 and drive it and the two sprockets 40 and 42. Withthe high-speed clutch 68 in disengaged condition as described above,drive will be through the low-speed sprocket 40 and the low-speed chain100 to the low-speed driven sprocket 60. Such low-speed driven sprocket60 will then rotate the outer clutch element 63 in a forward-drivedirection relative to the jackshaft, and the roller clutch 64 willengage and transmit driving torque to the jackshaft 48. The jackshaft 48will rotate the drive sprocket 52 to transmit drive to the rear wheel 26of the minibike at the low-speed ratio determined by the relative sizesof the low-speed sprockets 40 and 60.

For high-speed drive, after the low-speed drive has accelerated the biketo a satisfactory speed, the operator decelerates the engine and pullsout the knob 94 to retract the control foot 88 from the path of rotationof the rib 86 on the high-speed clutch control sleeve 84. This releasesthe leading end of the clutch spring 74 for its normal clutching action.Forward rotation of the high-speed driving element 70 by the sprocket 62will then cause the spring 74 to wind up on the clutch surfaces 72 and78 to clutch the driving and driven elements together. The jackshaft 48will then be driven by the high-speed sprocket 62 at a speed determinedby the size ratio of the high-speed sprockets 42 and 62, and faster thanthe lowspeed sprocket 60. The low-speed roller clutch 64 will thenoverrun to allow the jackshaft 48 to rotate at the higher sped, and thehigh-speed drive will be transmitted to the drive sprocket 52 and therear wheel 26.

Since both clutches 64 and 68 have overrunning properties, they will notbe capable of transmitting drive from the rear wheel to the engine shaft14, and the connection will not permit the engine to act as a brake forthe bike. The drive train will however, provide a positive driveconnection between the rear wheel and the brake drum 54, and amplebraking action will be obtained by tightening the brake band 56 aboutsuch drum 54 by means of the brake control handle 98 and its controlcable 96.

The two-speed transmission may be embodied as original equipment on thebike by equipping the bike frame with a jackshaft-mounting tube 46 andmounting the jackshaft 48 in such tube in the manner shown anddescribed.

The two-speed transmission can also be provided as a conversion of abike not so equipped. If the bike has ajackshaft, the original jackshaftmay be replaced by the jackshaft 48 of the present invention. Where thebike does not have a jackshaft and jackshaft mounting, the kit shown inFIG. 2 may be used. The engine is loosened from its mounting and theplatform 44 of the mounting bracket is inserted between the engine andits original platform mounting. This will provide the jackshaft-mountingtube 46, and connections can be made as shown in FIG, 2 and describedabove.

The arrangement of FIG. 2 places the drive sprocket 52 on the oppositeside of the bike from the projecting end of the motor drive shaft 15,and some modification may be necessary if the rear wheel has itssprocket on the same side of the bike as the projecting end of the motorshaft 15. Either of two modifications may be used. One modification isto reverse the position of the rear wheel 26 to place its sprocket onthe opposite side. The other modification is to transfer the drivesprocket 52 from the remote end of the jackshaft 48 as shown in FIG. 2to the near end of such jackshaft, between the lowspeed sprocket 60 andthe adjacent bearing 50.

lclaim:

1. A two-speed drive for a motorbike having an engine shaft, a jackshaftand a drive wheel, adapted to be positively controlled by the operatorof the motorbike, comprising high-speed and low-speed drive sprocketsmounted for rotation by said engine shaft,

high-speed and low-speed driven sprockets or transmitting drive to thedrive wheel, mounted on said jackshaft and connected respectively tosaid drive sprockets to provide high-speed and low-speed drive trains,

said low-speed driven sprocket being connected to the jackshaft by anoverrunning clutch arranged to overrun when the high-speed drive trainis engaged,

said high-speed driven sprocket being connected to the jackshaft by adisengageable high-speed clutch,

and operating means arranged for positive control by the operator todisengage said high-speed clutch and thereby cause the low-s eed drivetrain to become 0 erative,

said disengageab e clutch comprising a riving clutch member rotatablymounted on the jackshaft with the high-speed driven sprocket, a drivenclutch member fixed to the jackshaft, said driving and driven clutchmembers having aligned cylindrical clutch surfaces, and a coil springengaged with said clutch surfaces and wound in a direction to clutch thesame together for forward drive transmission, and said operating meanscomprising blocking means to block rotation of the leading end of saidclutch spring to disengage the same from both clutch surfaces.

2. A two-speed drive according to claim 1 with the addition ofacentrifugal clutch having a shoe assembly mounted on the engine shaftand a clutch drum rotatably mounted coaxially with and engageable by theshoe assembly, the drive sprockets being mounted for rotation with theclutch drum.

3. A two-speed drive according to claim 1 with the addition of means toconnect the jackshaft in positive drive relation to the drive wheel, abrake rotor on the jackshaft and means for braking said rotor to applybraking effort in the drive train between said clutches and the drivewheel.

4. A kit for providing an operator-controlled two-speed drive for amotorbike having a frame, an engine support, an engine having a shaft,and a drive wheel, comprising an engine platform adapted to be mountedon the engine support of the motorbike and to receive the enginethereon, a high-speed drive sprocket and a low-speed drive sprocketadapted to be mounted on and driven by the engine shaft,

jackshaft bearings fixed to the platform in position to mount ajackshafton an axis between the engine and the drive wheel, ajackshaft mounted insaid bearings, a lowspeed driven sprocket mounted on said jackshaft andoperatively connected thereto by an overrunning clutch adapted to permitthe jackshaft to overrun said driven sprocket in the forward drivedirection of rotation thereof, a high-speed driven sprocket mounted onsaid jackshaft and operatively connected thereto by a disengageableclutch,

and operating means adapted for positive control by the operator foractuating said disengageable clutch between engaged and disengagedconditions.

5. A two-speed drive kit according to claim 4, further comprising amounting bracket including said engine platform adapted to be mounted onthe engine support of the motorbike and to receive the engine thereon,and

a bearing tube transversely fixed to the bracket in position to liebetween an engine received on the platform and the drive wheel of thebike,

said jackshaft bearings being mounted in said bearing tube.

6. A two-speed drive kit according to claim 4, further comprising abrake support bar fixed to said bracket and projecting beyond saidbearing tube in offset relation to its axis,

a brake rotor on the jackshaft, and

a brake mean carried by said bar for applying braking effort to thebrake rotor.

1. A two-speed drive for a motorbike having an engine shaft, a jackshaftand a drive wheel, adapted to be positively controlled by the operatorof the motorbike, comprising high-speed and low-speed drive sprocketsmounted for rotation by said engine shaft, high-speed and low-speeddriven sprockets or transmitting drive to the drive wheel, mounted onsaid jackshaft and connected respectively to said drive sprockets toprovide high-speed and low-speed drive trains, said low-speed drivensprocket being connected to the jackshaft by an overrunning clutcharranged to overrun when the highspeed drive train is engaged, saidhigh-speed driven sprocket being connected to the jackshaft by adisengageable high-speed clutch, and operating means arranged forpositive control by the operator to disengage said high-speed clutch andthereby cause the low-speed drive train to become operative, saiddisengageable clutch comprising a driving clutch member rotatablymounted on the jackshaft with the high-speed driven sprocket, a drivenclutch member fixed to the jackshaft, said driving and driven clutchmembers having aligned cylindrical clutch surfaces, and a coil springengaged with said clutch surfaces and wound in a direction to clutch thesame together for forward drive transmission, and said operating meanscomprising blocking means to block rotation of the leading end of saidclutch spring to disengage the same from both clutch surfaces.
 2. Atwo-speed drive according to claim 1 with the addition of a centrifugalclutch having a shoe assembly mounted on the engine shaft and a clutchdrum rotatably mounted coaxially with and engageable by the shoeassembly, the drive sprockets being mounted for rotation with the clutchdrum.
 3. A two-speed drive according to claim 1 with the addition ofmeans to connect the jackshaft in positive drive relation to the drivewheel, a brake rotor on the jackshaft and means for braking said rotorto apply braking effort in the drive train between said clutches and thedrive wheel.
 4. A kit for providing an operator-controlled two-speeddrive for a motorbike having a frame, an engine support, an enginehaving a shaft, and a drive wheel, comprising an engine platform adaptedto be mounted on the engine support of the motorbike and to receive theengine thereon, a high-speed drive sprocket and a low-speed drivesprocket adapted to be mounted on and driven by the engine shaft,jackshaft bearings fixed to the platform in position to mount ajackshaft on an axis between the engine and the drive wheel, a jackshaftmounted in said bearings, a low-speed driven sprocket mounted on saidjackshaft and operatively connected thereto by an overrunning clutchadapted to permit the jackshaft to overrun said driven sprocket in theforward drive direction of rotation thereof, a high-speed drivensprocket mounted on said jackshaft and operatively connected thereto bya disengageable clutch, and operating means adapted for positive controlby the operator for actuating said disengageable clutch between engagedand disengaged conditions.
 5. A two-speed drive kit according to claim4, further comprising a mounting bracket including said engine platformadapted to be mounted on the engine support of the motorbike and toreceive the engine thereon, and a bearing tube transversely fixed to thebracket in position to lie between an engine received on the platformand the drive wheel of the bike, said jackshaft bearings being mountedin said bearing tube.
 6. A two-speed drive kit according to claim 4,further comprising a brake support bar fixed to said bracket andprojecting beyond said bearing tube in offset relation to its axis, abrake rotor on the jackshaft, and a brake mean carried by said bar forapplying braking effort to the brake rotor.